With rising public awareness to environmental protection, healthy living, physical fitness and depletion of natural resources, more and more people opt for the pollution-free, less resource-consuming while good-for-your-health bicycle as a preferred mode of transportation and exercise to replace the energy-consuming and air polluting motorcycles and cars.
Multi-speed bicycles currently available on the market mostly achieve speed change by using a shift lever to control movement of derailleur mechanism that guides the chain to engage one of a number of chain wheels of different sizes. It is also known to use a transmission installed in bicycle hub that enables a shift between high and low gears by driving the reverse rotation of chain wheels. The known transmission mechanisms typically achieve only two-speed gear shift or have the drawbacks of complicated mechanism, high-cost or slow response to gear change so that further improvement is warranted.